If we place an order in an online store we are often thrilled how fast the parcel is delivered to our doorstep. This is possible because logistic companies have established a very reliable and efficient system to distribute ...

About 85-90 per cent of the cancer cells have the wrong number of chromosomes. But how do they survive and develop under these conditions? WWTF-"Young Investigator" Christopher Campbell and his team will trace the basic causes ...

Each cell in a woman's body contains two X chromosomes. One of these chromosomes is switched off, because nobody can live with two active X chromosomes. Hendrik Marks and Henk Stunnenberg, molecular biologists at Radboud ...

In female mammals, one of the two X chromosomes is inactivated. Thanks to research using special stem cells, geneticists at ETH Zurich have been able to provide detailed insight into the molecular mechanism behind this inactivation ...

Alexander Godfrey, a PhD student in biology at MIT, is acutely fascinated by the Y chromosome, which confers maleness. This chromosome is often considered a genetic castaway—because its complexity makes it very difficult ...

Researchers at the University of Tokyo have discovered a long-overlooked process important for converting a long, string-like DNA molecule into a chromosome. This finding gives us a better understanding of the mechanism of ...

For the first time, a team of scientists, led by Prof. Axel Janke of the Senckenberg Research Center for Biodiversity and Climate, reconstructed part of the male chromosome in polar bears. The scientists were able to assign ...

Canadian and British researchers have discovered that chromosomes play an active role in animal cell division. This occurs at a precise stage - cytokinesis - when the cell splits into two new daughter cells. It was observed ...

Chromosome

A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes. Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000 nucleotides in a long chain. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.

In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes are the essential unit for cellular division and must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, whereas duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right). Chromosomal recombination plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may aberrantly evade apoptosis leading to the progression of cancer.

However, in practice "chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.